This work is directed at contributing to knowledge of paramyxovirus structure and replication. Agents being studied are Newcastle disease virus (NDV), Sendai virus, mumps virus, and Yucaipa virus. Specific objectives are: (1) To characterize viral genomic RNAs and single- stranded virus-specific complementary RNAs appearing in infected cells, and viral structural proteins. Methods include radioisotopic labeling with specific precursors, sucrose gradient centrifugation, acrylamide gel electrophoresis, chromatography and nucleic acid hybridizations. (2) To determine if paramyxovirus complementary RNAs are messenger RNAs, arising from transcription of viral genomes. We will test whether polypeptides synthesized in a cell-free protein synthesizing system contain peptides identical to peptides in viral structural proteins. (3) To obtain temperature-sensitive mutants of Sendai virus, for exploring structural and functional relationships of subgenomic viral RNAs and viral genomes by genetic complementation tests and RNA hybridizations.